Fiber optic sensing systems may be used to monitor downhole parameters such as vibrations, acoustics, pressure, and temperature changes. One example sensing system is referred to as distributed acoustic sensing (DAS). In a DAS system, an interrogation beam is conveyed along an optical fiber, and interferometric techniques are applied to perform phase analysis of backscattered light. The phase information of backscattered light can be correlated with acoustic activity at points along the optical fiber. The quality of the acoustic information obtained is therefore dependent on the accuracy of the phase analysis.
One way to perform phase analysis involves two auxiliary signals that have a relative phase-shift of 90°, called in-phase and quadrature signals (I/Q). However, imperfections of the involved optical components cause various issues, coined “I/Q imbalance,” such that straightforward extraction of phase information from I/Q data is usually not possible. Example I/Q imbalance issues include time-varying effects such as a DC offset as well as an amplitude and/or phase mismatch between the received I and Q signals. Such I/Q imbalance issues affect the accuracy of subsequent digital signal processing algorithms to recover phase information or related parameters.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.